The invention relates to a display device as defined in the precharacterizing part of claim 1.
The invention further relates to a lenticular screen for use in a display device.
The display device is used for displaying television and graphic images.
The display device may comprise two or more liquid crystal display panels which are arranged next to each other for enlarging the physical size of the display, without enlarging the size of the display panels. In this way, a relatively cheap display is obtained. A seam is present at the neighboring sides of the liquid crystal display panels. In order to reduce the visibility of the seam between the liquid crystal display panels, it is necessary to prevent light entering the seam area. This is achieved by a black mask, which is periodical across the entire display, and by the application of collimated light distribution. The collimated light distribution requires a lenticular screen which is optically coupled to the liquid crystal display panels for enlarging the luminance distribution of the display after the light has passed through the liquid crystal display panels.
The display device may have such a configuration of liquid crystal display panels that only vertical seams are present. Consequently, also the black mask has only a periodical vertical structure. In this type of display device, the requirements of the collimated light source in the vertical direction are less stringent and the lumen output or the luminance at the front of the display device can be increased. In order to obtain an increased lumen output of the display device, the widest possible collimating angle is chosen for which no grey scale inversion occurs in the vertical direction of the liquid crystal display device.
A disadvantage of the present display device is that this collimating angle will give rise to a viewing asymmetry in the horizontal direction.
It is an object of the invention to provide a display device with a reduced viewing angle asymmetry in the horizontal direction. This object is achieved by a display device according to the invention as defined in claim 1. The trapezoidal structure of the lenticular screen of the display device according to the invention mixes light rays traversing the liquid crystal panels at positive and negative angles about the normal in the second direction. The light rays coming from the different positive and negative angles will be totally reflected at the slanted sides of the trapezoidal structure, and the asymmetry of the luminance in the viewing angle in the second direction is averaged and will be reduced. The known lenticular screens only enlarge the luminance distribution but do not mix the light incident at oblique angles with respect to the normal of the lenticular screen, so that the asymmetry in the second direction is not reduced.
Advantageous embodiments of the display device according to the invention are defined in the dependent claims.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.